An Uncooled Infrared Microbolometer Array for Low-Cost Applications

Abstract

This letter describes the implementation of a low-cost $32\times 32$ uncooled infrared microbolometer array using a standard 0.5- $\mu \text{m}$ CMOS process and a surface sacrificial layer technique, in which the CMOS metal interconnection layers are used as the infrared sensitive material. The sacrificial layer embedded during the CMOS fabrication can be etched using a simple wet etching process following the CMOS processes, without the need for any lithography or material deposition steps. The CMOS metal interconnect layers are aluminum, with a temperature coefficient of resistance of 0.398%/K. The 32 $\times $ 32 focal plane array (FPA) has a pixel size of 65 $\mu {\rm m}\times 65~\mu \text{m}$ and a fill factor of 29%. The thermal conductance of the FPA was measured to be $3.47\times 10^{-6}$ W/K, with a thermal time of 3.85 ms, and a dc responsivity of 1050 V/W at a 10-Hz chopper frequency. The total measured rms noise of the microbolometer is 0.706 $\mu \text{V}$ for a 10-kHz bandwidth, resulting in a detectivity of $5.2\times 10^{8}$ cmHz $^{1/2}$ /W.